AbstractWith the further increase of human demand for energy, the development of renewable energy has become crucial. Photovoltaic (PV) technology, particularly solar cells (SCs), has emerged as a promising renewable energy source. However, to unlock the full potential of SCs, it is essential to address the challenges of reducing costs and improving device efficiency. This doctoral thesis focuses on crystalline silicon (c-Si) and perovskite solar cells (SCs), including dopant-free interdigitated back contact (IBC) SCs, Tunnel Oxide Passivating Contact (TOPCon) SCs, and perovskite SCs.
Firstly, the thesis explores the design principles and related mechanisms of dopant-free IBC SCs. Numerical simulations reveal that device efficiency can be improved by optimizing the device pitch and area fill ratio, or by reducing surface recombination at the electron transport layer and n-Si interface. The impact of passivation quality and contact resistance on efficiency is demonstrated, indicating the potential for achieving an efficiency exceeding 24%. Additionally, the thesis investigates Si surface passivation mechanisms induced by electric fields inherent to the dielectric films and examines the impact of device properties on IBC SCs through well-designed numerical simulations.
Secondly, the thesis combines elaborate simulations with experiments to uncover the physical mechanism of polycrystalline silicon (poly-Si)/silicon oxide (SiOx)/c-Si contacts. Numerical simulations are employed to review the charge-carrier transport mechanism in poly-Si/SiOx/c-Si contacts, suggesting that the tunneling and pinhole transport mechanisms are present and interact with each other. A fundamental physical model that considers passivation and contact behavior simultaneously is established to evaluate the potential efficiencies of devices. Proof-of-concept devices with complete cell structures demonstrate high efficiencies, averaging beyond 23.5% for the annealing temperature of 820°C, indicating the combined effect of passivation and contact properties on device performance.
Thirdly, an advanced optical design by texturing the front-side glass using a gradient index Gaussian-type structure is proposed for PSCs. Numerical simulations show that this design exhibits a broadband light-harvesting response, resulting in a remarkable photocurrent density of 23.35 mA/cm². The optical absorption and loss distributions are analyzed, suggesting that Gaussian-type structures can effectively reduce reflection loss to 2.55 mA/cm². Furthermore, a comprehensive model is developed by coupling the traditional photoelectric model of free charge-carriers with the ion model and photon cycling (PR) model to simulate the carrier generation/transmission/recombination process of IBC PSCs. Simulation results indicate that: 1) IBC PSCs can achieve higher current density than ordinary sandwich PSCs due to reduced parasitic absorption loss; 2) optimized parameters can lead to cell efficiencies exceeding 25%; 3) mobile ions, with a concentration greater than 1016 cm−3 , play a crucial role in altering the energy band, free carrier distribution, and spatial electric field within the perovskite layer, thereby influencing cell efficiencies; 4) the introduction of PR effect can effectively enhance the open-circuit voltages and device efficiencies.
|Date of Award
|1 Mar 2024
|Jim Greer (Supervisor) & Guang Zhu (Supervisor)